The invention relates to a method for detecting the position and the direction of motion of a movably mounted part that can be used in particular for the externally powered adjustment of closing parts in motor vehicles, e.g. on an electrically driven window lifter with an anti-jamming function.
Known devices for the detection of position and direction of rotation make use of two-channel sensor systems whose signals are phase-shifted and evaluated in an electronic unit. The sensors used can operate in accordance with very different physical principles (e.g. electrical, magnetic, inductive, optical).
For example, the electric motor drive specified in EP 0 359 853 A1 makes use of two Hall sensors displaced at an angle to each other and allocated to a ring magnet attached to the armature shaft. When the armature shaft rotates, the Hall sensor generates two correspondingly phase-shifted signals that are digitized and then evaluated in an electronic unit and thereafter represent the only foundation for identifying the direction of rotation. Since the corresponding signal pattern is characteristic (different) for each direction of rotation, the count pulses can equally be uniquely assigned to a direction of rotation.
Because the known technical solution requires no fewer than two sensor channels, however, it needs a correspondingly high number of components and conductors for its implementation. Also, the construction space is to be kept free for it can have a negative effect, especially when using small drive units with integrated electronics.
From JP 63-30 43 07 A, a velocity control for a motor drive is known where the phase difference between a velocity control pulse and the incremental pulse of a laser length measuring device is continuously acquired. The control loop used also has a pulse converter and a mechanism for transforming the rotary motion of the motor into a linear motion. An up or a down signal is generated in a transformer from the measurement of the linear motion in accordance with the direction of the positioning command.
The solution described does indeed permit very accurate control of the adjustment velocity of an object but it is not suitable for establishing at the same time its position. Further measures must be provided for this purpose.
Furthermore, from DE 43 15 637 C2, a method for detecting the position and direction of rotation is known, where not only the signal edges of the digitized sensor signal but also the status of the drive is allowed for in that in the event of reversal of the direction of rotation the signal edges are assigned in accordance with an overshoot time that is limited by fixed time thresholds which can be determined empirically or calculated mathematically. Adaptation to the widely varying system conditions is not possible because the variation of the motor current over a period of time while the direction of rotation reverses varies by several orders of magnitude. In particular, a control with fixed thresholds is always limited only to a specific load case which is essentially determined by the mass moment of inertia to be overcome. A rise due, for instance, to a window pane freezing or jamming does lead to deviations. In motor vehicles, the operating supply voltage can certainly drop considerably if the battery is low and other load elements are also being operated. If the motor is used very frequently, as for example in the case of actuating drives on industrial machine tools, the electrical parameters of the motor also change because of the warming effect. If the time thresholds were to be placed so far apart that all these cases could still be measured, then a particularly smooth running actuator arrangement would perform several revolutions in the opposite direction before being detected by the threshold.
EP 0 603 506 A2 describes a method for determining with a position encoder the position of a part driven in two directions by an electric motor in motor vehicles, where a change in direction is to be identified according to the duration of a break period between two pulses from the position encoder. Errors can occur in such a method due to rapid change of direction or if the motion of the part is non-uniform and does not take place in step form in a single step.
It is also known that the behavior of d.c. motors can be described by means of an electromechanical motor state model based on the motor equations. The motor equation U.sub.q (t)=c.sub.2.multidot..PHI..multidot.n(t), also known as generator equation, and the motor equation M.sub.m (t)=c.sub.1.multidot..PHI..multidot.I.sub.M (t) as well as the electrical relationship ##EQU1##
is also to be found in literature, for instance Lindner and others: Reference material Elektrotechnik--Elektronik, Leipzig, 2. printing 1983, p. 199 ff. The reference symbols signify the following: U.sub.q induced voltage; c.sub.1, c.sub.2 motor constants; .PHI. magnetic flux; n rotational speed; M.sub.L load moment; M.sub.m motor moment; M.sub.B the acceleration moment resulting from the motor moment; I.sub.M motor current; U.sub.M motor terminal voltage; R.sub.a armature resistance; R.sub.k external terminal resistance; L inductance of the motor winding; J mass moment of inertia of the entire rotating arrangement including the parts to be moved, such as the windows, for example.